1. Field of the Invention
The present invention relates generally to the field of multi input multi output modem systems and particularly to a method and apparatus for using a flexible architecture to correct carrier offsets in the received signals.
2. Description of the Prior Art
As computers have gained enormous popularity in recent decades, so have networking the same allowing for access of files by one computer from another. More recently and with the advent of wireless communication, remote and wireless networking of computers is gaining more and more notoriety among personal users, small and large business owners, factory facilities and the like.
With regard to the wireless networking of personal computers including laptops, a particular modem, namely modems adapted to the IEEE 802.11a or 802.11g industry standard, are commonly employed. That is, an antenna is placed inside or nearby the personal computer and an RF chip receives signal or data through the antenna and an analog-to-digital converter, typically located within the personal computer (PC), converts the received signal to baseband range. Thereafter, a baseband processor is employed to process and decode the received signal to the point of extracting raw data, which may be files transferred remotely and wireless, from another PC or similar equipment with the use of a transmitter within the transmitting PC.
There are several prior art apparatus and techniques for implementing 802.11a/g modem receivers, however, such prior art have not successfully utilized the fullest potential of the 802.11a/g modem. For example, the maximum rate of this type of modem device is 54 Mbits/sec, but in the presence of multi-path channel, use of current prior art methods and apparatus does not allow for reception of data at such rates. In fact, successful reception of data under multi-path channel conditions currently takes place at lower rates or may fail altogether.
To improve reception of data at higher rates multi input multi output orthogonal frequency division multiplexing (OFDM) transceivers having multiple antennae for transmitting and receiving OFDM-modulated data packets is often employed. In OFDM modulation with considerable sensitivity to carrier offsets, the quality of the received signals depends to a large extent on the orthogonality between the adjacent subcarriers. The presence of residual carrier offsets in the received baseband signals may result in inter-carrier interference (ICI) which quickly degrades signal quality. The presence of carrier offset is particularly critical for multi input multi output modem systems wherein decoupling of several data streams received by multiple receiver antennae is performed. If the carrier offset (or carrier frequency offset) is not completely removed from the independent received signals, insufficient decoupling of the data streams may result which further degrades the signal quality. Thus, it is desirable to develop a method and apparatus for multi antennae multi input multi output transceivers that offer improved performance over the conventional designs without incurring substantially higher costs.